The use of measurement methods and the use of coordinates in photogrammetric projects give the three-dimensional resource of the point cloud or polygonal mesh resulting from the processing a closer approximation to the captured element, respecting the proportions of the element.

Georeferencing by taking natural physical points or targets gives greater rigour to the model, giving it a scientific value as a non-ideal reflection but as a copy of reality, since the choice of X,Y,Z points applied to the three-dimensional model firstly orientates the model, giving it its predefined place in space and secondly scales the model to copy and capture the real distances between the different points, reflecting the dimensions and volume of the three-dimensional model itself.

Georeferencing can be carried out by different methods, either aerial or terrestrial, depending on the tools used, and the accuracy will also vary in this way. In professional surveying work, surveys usually have an accuracy of 20mm+-1ppm.

Before starting the work, it is important to know the framework of the geographic coordinates used in the different tools, to avoid possible later calculation errors, so it is of vital importance for the project to work in all its processes with the same system of coordinates and location.

The most widely used geographic coordinate and latitude/longitude location system is the WGS84 or World Geodetic System 1984, which is used on a global scale, providing the opportunity to geolocate every point on the earth on the X and Y Z axes. In many places, local coordinate systems are gaining in importance.

The use of the European Terrestrial Reference System 89 or ETRS89 is promoted in the EU, as well as in coordinate detection products and specialized GPS. This datum is not only compatible with the European GALILEO navigation system, but also with GPS and GLONASS, which means that it is possible to operate on the European continental plate with any of the above systems.

There are a variety of methods for obtaining 3D geospatially-rectified models, using GIS systems, obtaining products such as the raw three-dimensional model itself, the orthomosaic resulting from the previous one with orthorectification adjustments to eliminate the distortions that the human eye and the camera as an imitation of this produces. All this work is obtained by means of physical and digital control points (Markers).

Any visible object placed or not for that specific purpose. With the creation of this data, a large amount of metadata is generated that allows its subsequent use in contour lines and histograms among other analysis tools that reveal different types of constituent data of the terrain, section or chosen area.

It is possible to obtain products such as MDS or DTM: to generate greater results such as contour lines, analysis of watercourses, slopes, gradients, unevenness, among others:

• (DSM): DigitalSurfaceModel:These are digital models that represent the existing elements and shapes captured and digitized on the terrestrial surface subjected to the process, such as buildings, or the relief of the terrain itself such as mountains and elements that make them up, such as trees.
• (DTM): DigitalTerrainModel:These are digital models that represent the shape of the terrain, once the extraordinary elements such as vegetation or infrastructures have been removed, eliminating all elements that are not part of the terrain itself.

With these high-information digital models it is also possible to generate photogrammetrically rectified orthomosaics for the analysis of different studies or interventions in the field.